Very sorry to read this. While every situation is different (and changing) here a link to a post that might provide some useful information for you.

What do I do if I think my husband is having a midlife crisis? (note that this is part one though the post contains a link to part ii).

With regard to your specific question, there is of course no good answer. While divorce rates are tracked, divorces from "midlife crisis" are not and when you do see figures they are suspect because there is no standardized diagnosis for midlife crisis. Finally, even if you did have the statistic it would be for a population as opposed to your unique situation.

What we can tell you, albeit anecdotally and unscientifically, is that there are many, many situations where the marriage does remain intact especially when you've made it as long as you have (18 years).

Wesley Hein
Wesley [at] lifetwo [dot] com